The present invention relates to a solid-state laser device for producing laser light by optically pumping a solid-state medium.
In general, a solid-state laser device has a laser rod as a solid-state laser medium and adapted to produce laser light by optically pumping the laser rod. If the laser rod is arranged within an optical resonator, laser light produced from the laser rod is amplified by the optical resonator to produce an oscillation output.
As a pump light source for optically pumping the laser rod, an arc lamp, flash lamp, semiconductor laser, etc., are known and, recently, a semiconductor laser can be often used for outputting pumped light of a given wavelength absorbed in the laser rod. By doing so, it is possible to optically pump the laser rod effectively.
As a high-output semiconductor laser commercially available on the market, use is made of a stacked unit comprised of a plurality of low-output semiconductor lasers mounted as a stack array and each having a small light emitting section. For this reason, such high-output semiconductor laser has a plurality of such light emitting sections and hence an adverse effect is exerted on output beams obtained. If, in particular, in order to enable pumped light of a greater broadening angle from the semiconductor laser to be losslessly incident on the laser rod, a collimating lens is arranged near the light emitting section whereby the broadening angle of the pumped beam is suppressed, then a pattern (light beam) of the pumped lights to be directed toward the laser rod is splitted into a plurality of beams.
Therefore, the laser rod cannot be uniformly pumped with the pumped beam output from the semiconductor lasers, thereby producing a local stress concentration and temperature distribution and hence causing a damage to the laser rod. As a result, laser light from the laser rod has its intensity distribution made not uniform depending upon the pumped state. Further, there arises a local heat lens action, thus leading to a fall in quality of the beam.
In order to avoid such a problem, as shown in FIG. 1, a tube 2 has a laser rod 1 held therein and a cooling medium flown therethrough to cool the laser rod 1 and has a diffusion surface 3 formed on an outer peripheral surface thereof. And the tube 2 is inserted in an insertion hole 5 in a diffusion plate 4 and four tapered light guide passages 6 are formed in the diffusion plate 4 at 90.degree. intervals around the circumference of the tube 2. Beams P pumped from a corresponding semiconductor laser 7 pass through the corresponding light guide path 6.
Therefore, the beams P passing through the light guide passages 6, while being reflected on the inner surface of the light guide passage 6, are incident on a diffusion surface on the outer periphery of the tube 2. The beams, being diffused on the diffusion surface 3, are transmitted through the tube 2 to optically pump the laser rod 1.
According to such a structure, the beams P directed toward the laser rod 1 are diffused on the light guide passage 6 and diffusion surface 3 and it is, therefore, possible to optically pump the laser rod 1 by the beams P from the semiconductor laser.
Since, however, those beams P directed past the light guide passage 6 to the diffusion surface 3 on the tube 2 was liable to be reflected on the diffusion surface 3, a greater loss was involved due to the reflection of the pumped beam P and a fall in pumping efficiency was sometimes encountered. There were sometimes the cases where the diffusion plate 4 produced heat by the beams reflected on the diffusion surface 3 and, in addition, a heat transformation occurred on the diffusion plate 4. In order to prevent such heat transformation it was sometimes necessary to cool the diffusion plate 4.
It has also been considered that, as another means, a diffusion surface is formed on an outer periphery of the laser rod whereby beams are diffused. In this case, since it is not possible to adequately take a diffusion distance of the beams on the diffusion surface, the beams incident on the laser rod are less likely to be diffused, thus failing to uniformly pump the laser rod.